The document U.S. Pat. No. 6,387,078 pertains to an automatic injection apparatus which injects a single, pre-measured dose of stored medicine intramuscularly or transdermally, and the injection apparatus automatically retracts the hypodermic needle into the device after the injection is completed. The user presses the distal end i.e. the needle end, of the device onto the desired injection site and presses the actuation button. This releases the plunger-syringe-combination from its temporary engagement with the housing. The plunger-syringe-combination together with the spring-to-plunger-coupling are then forced away from the proximal end, i.e. the actuation end, of the housing by an energized driver spring. The driver spring propels the plunger-syringe-combination forward through the bore of the housing until the hypodermic needle exits the housing, and enters the recipient's tissue, and the syringe barrel touches the interior distal end of the housing. During this movement, a return spring positioned between the syringe assembly and the fixed, distal end of the housing becomes compressed and energized. When the liquid of the automatic injection apparatus is discharged by the plunger being pushed forward through the interior of the syringe barrel, the spring-to-plunger-coupling comes into contact with a splitter which disengages the driver spring from the plunger. Without the influence of the driver spring upon the plunger-syringe-combination, the energized return spring forces the plunger-syringe-combination to retreat rearward towards the proximal end of the device until the hypodermic needle is fully retracted into the housing.
As this automatic injection apparatus is directed toward injections of a pre-measured dose of stored liquid medicine where the plunger during injection pushes the liquid dose of stored medicine out of the apparatus, the solution will not be applicable for use when inserting an injection device as the handling and injection of a liquid under sterile conditions necessitates a complicated injection apparatus which need to interact with the liquid.
WO 2005/046780 (FIG. 97-102) describes a device used for automatic insertion of a cannula of an infusion device into the skin of a patient, and afterwards automatic retraction of the insertion needle. The insertion device has the form of an oblong cylinder (length≈4× diameter) which is open in one end (1984) and provided with means for activation at the other end (1952). When the infusion set has been loaded onto the needle (1968) the lock member (1962) is moved in direction of the end provided with means for activation by the patient using projections (1974) which projections are accessible through a slot (1976) of the housing until barbs (1956) of the lock member (1962) engage an outer surface of the housing (page 26, I. 24-27). Then the open end (1984) is placed against the skin of the patient and the means for activation (1952) is activated. When activated shoulders (1954) on the means for activation engage, the barbs (1956) are pushed toward each other in order to disengage the barbs from the housing. When the barbs are clear of the housing the lock member, the needle hub, the retainer body and the associated infusion device are moved by a first spring in direction of the open end (1984). The inserter device moves the infusion device towards the skin of the patient thereby inserting the needle and the cannula of the infusion device. As the cannula is fully inserted, barbs (1964) of the needle hub (1965) engage ramped surfaces (1972) of the sleeve (1982), causing the barbs (1964) to be forced toward one another. When the barbs (1964) have been forced sufficiently inwardly to clear ends (1988) of the main body (1980), the second spring (1966) then moves the needle hub (1965) in the direction of the activation means (1952). Thus the needle is removed from the infusion device leaving the infusion device in place on the skin while the retainer body remains in a position adjacent the open end of the sleeve so that once the insertion device is removed from the skin of the patient, the retainer body protects the patient from further contact with the needle.
This insertion device is rather complex and the length of the device is defined by the individual units forming the functional parts of the device as these units have to be placed more or less end to end. A feature illustrating the complexity of the unit is the fact that the two springs respectively biases the housing from the lock member and the retainer body from the needle hub while a main body is placed between the two spring systems to transfer the force from the first spring to the second spring.
According to the present invention the two spring units work directly together, as the first spring unit directly affects the movement of the carrier body while the second spring system is directly affected by the movement of the carrier body. That the spring units directly affect or is directly affected by the carrier body means that the spring units are connected to the carrier body directly or through a part which transfers the power either unchanged or under controlled modifications.